Scheduling the Hubble Space Telescope

Imagine using a telescope that is
orbiting
around the earth. How does one keep it pointed and
steady without the earth for support? What happens
if it points towards the moon or the sun? Who worries
about these things and makes sure the telescope doesn't
get damaged? One of the people is the Program Coordinator
(PC). The following notes were written by Mike Asbury
who was PC for the observations of NGC 4650A.

Under normal circumstances, when an
astronomer wants to use the Hubble Space Telescope
(HST) to observe an object in the sky, he/she submits
a proposal specifying what he/she would like to observe
and why HST is needed for such an observation. This
is submitted when the Space Telescope Science Institute
(STScI) issues a ``Call for Proposals''. The astronomer
is in "competition" with other astronomers for time
on the telescope. Thus, it is important for the astronomer
to stress the need for HST as opposed to ground-based
observations.

Once the proposal is submitted to STScI,
a panel of scientists review the proposal to see if
it truly warrants HST time and is technically feasible.
If the proposal is accepted, the astronomer is notified
and assigned two contact personnel at STScI. They
are assigned a ``Program Coordinator'' and a ``Contact
Scientist''. The Program Coordinator (PC) is the person
responsible for the overall scheduling of the observations.
The Contact Scientist (CS) is responsible for the
scientific aspects of the observation.

After the astronomer is notified that
his or her proposal has been accepted, the astronomer
must submit a more concise version of the proposal,
giving exact observing strategies. They do this through
software that is provided to them from STScI. Once
received by the PC, the proposal is processed to see
when the observations can be performed. Many aspects
can affect when an observation is performed. For instance,
the astronomer might want to observe the object at
only certain times of the year. Another aspect that
affects scheduling is the fact that the object cannot
be too close to the Sun or Moon, because those objects
are so bright that they may damage the instruments
on the telescope. Yet another aspect that affects
scheduling is acquiring ``guide stars''. These are
stars that HST ``lock'' onto to avoid drifting when
observing a target. If the target is in an area of
the sky where there are few stars or an overabundance
of stars, then acquiring guide stars may be a problem.

After all the scheduling issues are
worked out, the CS does a review of the proposal to
make sure all the scientific aspects of the observations
will be achieved without harming the telescope. Once
this is done, as it gets closer to the time that the
observations are to be performed, the observations
are put on a ``flight calendar''. This is a week long
calendar filled with observations. Flight calendars
are built three weeks in advance. After an observation
is put on a flight calendar, there is nothing left
for the PC, CS or astronomer to do other than sit
back and wait for the data.

Simple descriptions
of the work involved in operating HST are available
in the
Hubble Primer.